Gears have long been used in automobiles and other machines to transfer applied torque between components. Gears are often formed as wheels, worm wheels or linear racks incorporating protruding surfaces or teeth configured to engage cooperating surfaces within the assembly. Through this engagement, power is transferred between the components.
Gears are typically formed by casting or forging a desired gross shape from a suitable metal alloy and then cutting teeth by machining operations such as hobbing or shaving. Hardenable ferrous alloys are often used in the production of gears due to their ability to be hardened by heat treating techniques subsequent to initial formation. Heat treating is normally carried out by subjecting the machined part to an elevated temperature under a controlled treatment atmosphere rich in carbon and/or other treatment constituents for a predetermined period of time so as to allow infusion of the treatment constituents to at least a predefined depth. The part then normally undergoes an oil quench to lock in the heat treat characteristics. Such treatments substantially increase the surface hardness of the part.
The heat treating operations used typically leave layers of scale on the surface of the treated part. This scale may be made up of a combination of iron oxide, baked on oil, soot and other impurities. Such scale must be removed prior to the application of any protective coatings to the gear. In the past, it has been found difficult to efficiently clean the scale from gears to suitable levels for subsequent application of protective coatings without risk of damaging the gear surface.